The theoretical molecular weight of NaYF 4 :RE upconversion nanoparticles

Abstract

Upconversion nanoparticles (UCNPs) are utilized extensively for biomedical imaging, sensing, and therapeutic applications, yet the molecular weight of UCNPs has not previously been reported. Herein, we present a theory based upon the crystal structure of UCNPs to estimate the molecular weight of UCNPs: enabling insight into UCNP molecular weight for the first time. We estimate the theoretical molecular weight of various UCNPs reported in the literature, predicting that spherical NaYF4 UCNPs ~ 10 nm in diameter will be ~1 MDa (i.e. 106 g/mol), whereas UCNPs ~ 45 nm in diameter will be ~100 MDa (i.e. 108 g/mol). We also predict that hexagonal crystal phase UCNPs will be of greater molecular weight than cubic crystal phase UCNPs. Additionally we find that a Gaussian UCNP diameter distribution will correspond to a lognormal UCNP molecular weight distribution. Our approach could potentially be generalised to predict the molecular weight of other arbitrary crystalline nanoparticles: as such, we provide stand-alone graphic user interfaces to calculate the molecular weight both UCNPs and arbitrary crystalline nanoparticles. We expect knowledge of UCNP molecular weight to be of wide utility in biomedical applications where reporting UCNP quantity in absolute numbers or molarity will be beneficial for inter-study comparison and repeatability.

Long‐Term Colloidal and Chemical Stability in Aqueous Media of NaYF4‐Type Upconversion Nanoparticles Modified by Ligand‐Exchange

“…But this comes with several challenges like chemical and colloidal stability in aqueous media or the controlled functionalization by a defined number of receptor molecules . Most upconversion nanoparticles described in literature are consisting of a NaYF 4 host lattice as this materials has a preferable low phonon‐energy (≈300 cm −1 ) compared to other host materials like fluorides (LiYbF 4, ≈460 cm −1 ), oxides (Y 2 O 3 , ≈591 cm −1 ), or vanadates (YVO 3 , ≈890 cm −1 ). Therefore, it is not surprising that this host material together with Yb 3+ and Er 3+ has been used to design the most efficient upconversion nanoparticles .…”

In Situ Synthesis of Dicarboxylic Acid Functionalized Upconversion Nanoparticles for Bioimaging Applications

“…In the face‐centered cubic lattice arrangement (α phase), high‐symmetry cation sites are formed, where are randomly occupied by either Na + or RE 3+ ions ,. The structure of high‐symmetry cation sites results in higher probability of Er 3+ −Er 3+ cross relaxation.…”

“…On the other hand, it favours the population of the 4 F 9/2 energy level and thus greatly intensifies the red emission (Figure S3) . In hexagonal unit cells (β phase), there are two relatively low‐symmetry cation sites, which contain either Na + or RE 3+ ions ,. The structure of low‐symmetry cation sites drastically reduced the probability of Er 3+ −Er 3+ cross relaxation, so the green emission originated from the 4 H 11/2 → 4 I 15/2 and 4 S 3/2 → 4 I 15/2 transitions becomes dominant (Figure S4).…”

Selective cellular imaging with lanthanide‐based upconversion nanoparticles

“…The sample for the TEM was prepared by placing a drop of UCNPs suspended in water onto the surface of a holey carbon‐coated Cu grid and letting the water evaporate prior to imaging. The size distribution of nanoparticles was estimated from TEM images by using a custom MATLAB algorithm (MATLAB 2016a), based upon a circular Hough transforms to detect the pseudo‐spherical UCNPs . The diameter of the nanoparticle in pixels was subsequently converted to nanometer (nm) by known scale calibration of the HRFE‐TEM.…”